Fix usage of go:linkname

[ncruces]

go-sqlite3/internal/util/mmap.go

Lines 94 to 98 in aa7edb1

	// We need the low level mmap for MAP_FIXED to work.
	// Bind the syscall version hoping that it is more stable.
	//go:linkname mmap syscall.mmap
	func mmap(addr, length uintptr, prot, flag, fd int, pos int64) (*byte, error)

This is being worked on:
golang/go#56123
golang/sys#197

Goal is to fix it in time for Go 1.23.

[ncruces]

cc: @NyaaaWhatsUpDoc @daenney